This session shows that Apache Maven and their plugins work well on all Java versions, even on the early access releases. The critical parts are related to bytecode parsing and this session explains why and how to solve this.

1. Keeping up with Java
made easy with
Apache Maven
ROBERT SCHOLTE
@RFSCHOLTE / @ASFMAVENPROJECT

2. Moving Java Forward Faster (2017/09/06)
Proposal
Taking inspiration from the release models used by other platforms
and by various operating-system distributions, I propose that after
Java 9 we adopt a strict, time-based model with a new feature
release every six months, update releases every quarter, and a long-
term support release every three years.
Source: https://mreinhold.org/blog/forward-faster#Proposal

3. Surprise?
http://openjdk.java.net/projects/jigsaw/spec/minutes/2017-05-18

4. Feature driven schedule
20192006 2008 2010 2012 2014 2016 2018
Java 6
December 2006
Java 7
July 2011
Java 8
March 2014
Java 9
September 2017

5. Time driven schedule
20212018 2019 2020 2021
Java 10
March 2018
Java 11
September 2018
Java 12
March 2019
Java 13
September 2019
Java 14
March 2020
Java 15
September 2020
Java 16
March 2021

6. Is there really an issue?
Let’s see…

7. 3
6
6
6
7
JAVA 8
JAVA 9
JAVA 10
JAVA 11
JAVA 12
Java support
Classes Sources

8. Maven runtime versus toolchains
❖ JAVA_HOME is used for the Maven runtime
❖ For ease, JAVA_HOME is the default JDK
❖ With Maven Toolchains some plugins can get an explicit JDK
❖ Most reliable setup: toolchain

9. #RunsFineOnJDK9
#WorksLikeHeavenOnJDK11
❖ For Maven: YES!
❖ For the plugins: it depends… (most are fine!)

10. Sourcecode parser
QDox:
❖ reads model up to method signatures
❖ is less critical due to close to no language changes at this level

11. Bytecode parser
ASM:
❖ reads entire class, must know bytecode version
❖ is very critical, will now be updated every 6 months

12. 20182014 2015 2016 2017 2018
Java 9-ea
8 Apr '14
Java 9
22 Sep '17
Java 10
20 Mar '18
Java 11
25 Sep '18
Jigsaw ea
3 Nov '14
Releases of Java after 2014

13. Java 9 / Jigsaw early access
❖ Jigsaw team
❖ Java community
❖ Maven team

14. 2018
Today
2014 2015 2016 2017 2018
Java 9-ea
8 Apr '14
Jigsaw ea
3 Nov '14
Java 9
22 Sep '17
Java 10
20 Mar '18
Java 11
25 Sep '18
Maven Compiler Plugin 3.6.0
26 Oct '16
Maven Compiler Plugin 3.6.1
13 Jan '17
Maven Compiler Plugin 3.6.2
26 Jul '17
Maven Compiler Plugin 3.7.0
1 Sep '17
Maven Compiler
Plugin 3.8.0
26 Jul '18
Releases of Maven Compiler Plugin

15. Maven Compiler Plugin 3.5.1
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.5.1</version>
<configuration>
<compilerArgs>
<arg>-verbose</arg>
<arg>-Xlint:all,-options,-path</arg>
</compilerArgs>
</configuration>
</plugin>

16. Maven Compiler Plugin 3.6.x
First implementations of module path support for early adopters
Requirements:
❖ No changes to the pom.xml
❖ (Close to) no extra configuration for developers
Dependencies:
❖ ASM 6.0_ALPHA
❖ QDox 2.0-M6

17. Java 9 / Maven Compiler Plugin 3.7.0
Module Resolution moved to Plexus::Java
Dependencies:
❖ ASM 6.0_BETA
❖ QDox 2.0-M7

18. Plexus::Java
Maven independent library for general Java features
❖LocationManager
❖JavaVersion
Used by
❖maven-compiler-plugin
❖maven-javadoc-plugin
❖maven-jlink-plugin
❖maven-jmod-plugin
❖maven-surefire-plugin / maven-failsafe-plugin
❖…

19. 2018Sep Nov 2018 Mar May Jul Sep
Java 9
22 Sep '17
Java 10
20 Mar '18
Java 11
25 Sep '18
Maven Compiler Plugin
3.7.0
1 Sep '17
Maven Compiler Plugin
3.8.0
26 Jul '18
Releases of Maven Compiler Plugin

20. Java 10 / Maven Compiler Plugin ???
https://stackoverflow.com/questions/49398894/unable-to-compile-simple-java-
10-java-11-project-with-maven
Conclusion: no blocking issue

21. Updating ASM dependency
This implies: updating to latest asm-6.x dependency is possible,
but not to asm-7.x
Updating plugin dependencies already possible since Maven 2
ClassReader reader = new ClassReader( in );
reader.accept( new ClassVisitor( Opcodes.ASM6 )
{ … } );

22. 2018Sep Nov 2018 Mar May Jul Sep
Java 9
22 Sep '17
Java 10
20 Mar '18
Java 11
25 Sep '18
Maven Compiler Plugin
3.7.0
1 Sep '17
Maven Compiler Plugin
3.8.0
26 Jul '18
Releases of Maven Compiler Plugin

23. Java 11-ea / Maven Compiler Plugin 3.8.0
❖Reduce need for ASM
❖Use java.lang.module.ModuleDescriptor#read(InputStream)

24. Will Maven run on future JDK releases?
Yes, most likely
Even Apache Maven 3.0 (released 4 oct 2010) runs on 12-ea
Any issues are plugin related

25. Is it always forward compatible?
Yes in case of modulepath resolution
No for class analyzers (depend on ASM):
❖maven-dependency-plugin (analyze)
❖maven-plugin-plugin (descriptor)
❖maven-pmd-plugin (pmd)
❖maven-shade-plugin (minifyJar)

26. How do we test?
https://builds.apache.org/job/maven-box/

27. Conclusion
Java Release Train reveals critical chain of dependencies
A few plugins might not work right after a new Java release
Depending on the problem:
❖ Update related plugin dependency in your own project
❖ Patch plugin code (please create PR to help each other)

28. Questions?

29. Up-for-grabs
~60-80% of Java Project/Developers use Maven
The Apache Maven Project holds ~100 (sub)projects
Maintained by ~5-10 active volunteers (No Company!)
Let’s restore the balance!
https://s.apache.org/up-for-grabs_maven
https://maven.apache.org/guides/development/guide-committer-school.html

30. 20:00-21:00 BOF1
Apache Maven BOF
Robert Scholte
Karl Heinz Marbaise
Hervé Boutemy

31. Thank you
20:00-21:00 BOF1
Apache Maven BOF
Robert Scholte
Karl Heinz Marbaise
Hervé Boutemy